The optical-power generated by a laser-diode is primarily a function of junction temperature and current. During laser-diode operation the junction-temperature increases and the optical-power decreases.
Certain applications, such as computer-to-plate (CTP), require that the optical power is kept constant during the operation of the system. In order to prevent optical power variations, the system should be equipped with the ability to monitor either the optical power or the junction temperature; this will allow applying necessary corrections through appropriate modulation of the current.
Continuous power measurement is not recommended as it disturbs the beam path and accurate temperature measurements of the individual junctions are practically impossible for laser diode arrays. Thus, such measurements cannot be practically used to control the optical power of multiple emitters.